Netrebko and Hvorostovsky, Royal Festival Hall, London

It has been a very odd winter for celebrity concerts in London. There was Cecilia Bartoli flouncing around in velvet breeches pretending to be a castrato, Bryn Terfel whip in hand as the devil, Angela Gheorghiu trailing a little-known Romanian tenor and a fleeting appearance by Renée Fleming that was over almost before it had begun.